in certain frame, some game outputs more frames base on GPU clock speed + RAM clock speed alone because both GTX 1070Ti 2432 CUDA cores and 2560's GTX 1080 not fully utilize, while other game relies on stream processor count (nVIdia CUDA core), on <720p res the difference would be minimal, but at high res usually higher core count out pace lower core count, to prove this try manually set both GTX 1080 and GTX 1070Ti at 1.7GHz on one same PC and similar graphic preset.